Improved signal to noise ratio (SNR) and ease of use for magnetic resonance imaging (MRI) apparatus are needed to improve image quality and throughput in high-field MRI in research using small animal models. While linear-polarization (LP) mouse imaging has been demonstrated in a 500 MHz (11.7 T) vertical-bore magnet, available apparatus for vertical-bore magnets above 300 MHz is poorly suited for use with the physiologically monitored mouse or juvenile rat. Hence, most researchers prefer to use horizontal bore magnets, which are not widely available above 200 MHz and unavailable above 500 MHz. Prior work has demonstrated the unique contributions possible from our proprietary simulation software and patented coil technologies for both advanced gradients and circular-polarization (CP) MRI RF coils. We denote our rf coils "litz.cages", as they embody both paralleled conductor elements with insulated crossovers similar to that in our prior "ritz coil" technology and capacitively segmented phase shifts with four-point drive to achieve highly stable circular polarization. The litzcage has demonstrated order-of-magnitude improvement in tunability (ability to tune and match efficiently over a wide range of sample loading conditions). The proposed 24 mm 750 MHz RF coil is expected to provide a factor of 6 increases in SNR compared to the CP 200 MHz horizontal case, or a factor of 2.5 gains in SNR compared to the LP 500 MHz case. Our prior work has also established some essential requirements for rapid and convenient handling of physiologically monitored small animals in horizontal-bore magnets. The Phase I effort will also develop and construct a novel high-performance, water-cooled gradient coil of 47 mm bore compatible with 60 G/cm pulsed gradients at 19 T for use with the mouse RF coil and animal handling system. Field-testing of the Phase 1 750 MHz apparatus will begin early in Phase II at the Advanced MR Imaging and Spectroscopy Facility, McKnight Brain Institute, University of Florida, Gainesville, FL. The primary objectives are to achieve substantial improvements in resolution, convenience, and cost effectiveness for small-animal imaging in existing high-field vertical-bore magnets.